Multichannel telegraph system



May 12, 1942.

o. E. PIERSQN ETAL MULTICHANNEL TELEGRAPH 'SYSTEM Filed Dec. 8, 1939 12 Sheets-Sheet 1 I May'lz, 1942.

o. E; PlERsoN ETAL 2,282,341

MULTICHANNEL TELEGRAPH SYS TEM 12 Sheets-Sheet? Filed Dec. 8, 1939 May 12, 1942. o. E. PIERSON ETAL MULTICHANNEL TELEGRAPH SYSTEM Filed Dec. 8, 1939 12 Sheets-Sheet 3 9. oh .I.

INVENTORS E. PIERSON D. ADAMS SIZE GAR JR. ATT 'RNEY FIG..3

May 12; 1942. o. E. PIERSON ETAL MULTICHANNEL TELEGRAPH SYSTEM Filed Dec. 8, 1939 12 Sheets-Sheet 4 .I m 0: OF

2 3 INVENTORS 0.5. PIERSON MD. ADAMS BY AY- 9 7 .l 3 l 3 3 figlilGA R JR. M A ORNEY May 12, 1942. o. E. PiERSON ET AL MULTICHANNEL TELEGRAPH SYSTEM Filed Dec. 8, 1939 12 Sheets-Sheet 5 INVENTORS O E. PJERSQN M. DfA DAMS BY% GAR JR.

FIG. 5'

TO FIGJ May 12, 1942. o. RsoN ETAL MULTICHANNELYELEGRAPH S YSTEM Filed D619. 8 1939 l2 Sheets-Sheet 6 FIG. 6

May 12, 1942. o. E. PIERSCN ETAL MULTICHANNEL TELEGRAPH SYSTEM Filed Dec. 8, 1939' 12 Sheets-Sheet 7 INVENTORS O.E PIERSON M. .ADAM

i bRNE May 12 1942.- o. E. PIERSON s'rm.

v MULTICHANNEL TELEGRAPH S YSTEM INVENTORS O. E. PIERSON" M.D. ADAMS BY W S FIG. 8

R JR.

T RNE TO FIG. 8

May 12, 1942.

O. E. PIERSON ET AL MULT I CHANNEL TELEGRAPH SYS TEM Filed Dec. 8, 1939 12 Sheets-'She'et 9 All vvvv

May 12, 1942. o. E. PIERSON ETAL 2,232,341

MULT ICHANNEL TELEGRAPH SYSTEM Filed Dec. 8, 1939 v 12 Sheets-Sheet 1O FIG; IO

INVENTORS o. .PIERSON M. .ADAMS B GAR JR.

May 12, 1942. o. E. PIERSON ETAL MULTICHANNEL TELEGRAPH SYSTEM 12 Sheets-Sheet 11 Filed Dec. a,- 1939 CHAIN CONTROL FIG.

y 1942. o. E. PIERSON a-rm. 2,232,341

MULTICHANNEL TELEGRAPH SYSTEM Filed Dec. 8, 1939 12 Sheets-Sheet l2 m STOP REC. STOP 332 DISTANT HOME STOP STOP FIG. l3

PATTERN FAILUREflWQ INVENTORS O. E. PIERSON M. D. ADAMS W. W.EDGAR JR.

Patented May 12, 1942 MULTICHANNEL TELEGRAPH SYSTEM Oscar E. Pierson, Brooklyn, and Myron D. Adams and William Stanley Westerman Edgar, Jr., New York, N. Y., assignors to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Application December 8, 1939, Serial No. 308,226

28 Claims.

This invention relates to signalling systems and more particularly to expanding-channel or varioplex telegraph systems, the present application relating to an improvement upon the system disclosed and claimed in the prior patent to Pierson and Adams, No. 2,233,347, granted February 25, 1941.

The term expanding-channel or varioplex system as used herein refers to a system in which a variable number of telegraph transmitting subchannels share a common lane of traffic, substantially the entire lane time in the preferred system being divided among the operating transmitters or subchannels. The system thus distributes the use of the lane of trafiic which may consists of one or more channels of a synchronous multiplex system among any busy combination of a number of traffic sources or telegraph transmitters. While the lane of traffic referred to generally comprises a channel or channels of a multiplex system, any equivalent communication system may be utilized, such as one or more radio or carrier channels or one or more cable conductors or a direct wire or combinations of different types of communication channels. Hence, the expression lane of trafiic as used herein designates any suitable route or medium over which signalling is accomplished.

The expanding channel system thus comprises a multichannel system in which the number of subchannels operating over the connecting circuit or lane of traffic may be expanded or contracted by cutting in or out simultaneously transmitting and receiving devices at opposite ends of the system. The present invention relates particularly to aprinting telegraph system of this character in which message characters are sent from operating transmitters in sequence and printed on the corresponding receiving devices, one busy subchannel being rendered operative after another While omitting the idle or inoperative subchannels.

One object of the invention is to provide an improved control system for simultaneously cutting in or out the opposite ends of each subchannel when such subchannel has traffic to send or has completed the transmission of waiting trafiic.

Another object of the invention is to provide improved means for detecting failure of the control mechanism to cut in or out one end of a subchannel or to detect the falseor accidental cutting in or out of a subchannel.

Another object of the invention is to provide an improved channel switching system in which telegraph subchannels are connected to or disconnected from a transmission circuit or lane of traflic in response to switching signals and in which a plurality of channels may be controlled by a single group of impulses forming a single code combination.

Another object of the invention is to provide a channel switching system having improved means for detecting and/or controlling transmission in response to failure of the line circuit or connecting lane of traffic, or distortion of signals transmitted thereover.

Another object of the invention is to provide in a system of the character described means for automatically stopping transmission if a subchannel fails to be cut in or cut out in response to the proper control signal.

Other objects and advantages of the invention will appear from the following description of the preferred embodiment thereof shown in the ac companying drawings wherein:

Figs. 1 to '7, inclusive, form a circuit diagram of the transmitting apparatus at one end of the system;

Figs. 8 to 11, inclusive, form a circuit diagram of the receiving apparatus at the other end of the system; and

Figs. 12 and 13 are simplified diagrams illustrating certain features of the system.

It will be understood that the complete system ordinarily includes transmitting and receiving apparatus at each office, the receiving apparatus at the first ofiice being similar to that shown in Figs. 8 to 11, and the transmitting apparatus at the second office being similar to that shown in Figs. 1 to '7. I i

The system illustrated for the purpose of explaining the invention comprises a plurality of sources of signals represented by'tape transmitters (see Fig. 1) adapted to share three channels of a synchronous multiplex system and to operate corresponding printers at the receiving office (see Fig. 11). A relay chain is arranged to connect the operative transmitters one after the other to the multiplex system at' the transmitting office and a similar connector relay chain or mixer is provided for connecting the printers to the same channels of the multiplex'system at the same time at the receiving office. If three or less than three subchannels are in operation the connector relays'of the relay chain connect such subchannels to a corresponding number of multiplex channels and no stepping of the relay chainoccurs. If, however, more than three subchannels are in operation the connector relays operate in such sequence as to connect the operative subchannels one after the other to the three multiplex channels in a manner generally similar to the operation of the relay chain described in the above mentioned patent of Pierson and Adams.

The transmission apparatus is preferably operated at high speed for operating economy and efiiciency, and in a system of this character the connecting circuit may be of considerable length, for example, several hundred miles or more, and may include one or more telegraph repeaters. It will be obvious that in an extensive system of this character it is impossible to avoid occasional signal failures resulting from faulty circuits or apparatus or from atmospheric disturbancesior induction. Since the relay chains at the transmitting and receiving ofiioes must operate in synchonism and provide for the connection of varying numbers of subchannels, a signal must be transmitted to the receiving ofiice whenever a subchannel is to be cut in or out of service in order to effect this function simultaneously at both offices. Since this switching signal is transmitted over the same channel or lane of trafiic employed for communication and is similar in certain respect to the code signals used to control the receiving printers, the distortion or failure of a signal or group of code signals may cause either a false switching signal or the loss of a switching signal. Since this occasional failure cannot be avoided in actual practice at the high transmitting rates required for efiicient operation, it is necessary to provide means for detecting false switching signals or the failure of a switching signal. 1

In the system illustrated for the purpose of explaining the invention, switching signals are transmitted whenever a change in the subchannel pattern occurs and rotary step-by-step control switches are employed at the sending and receiving ofiices, respectively, for controlling the cutting in and out of subchannels from the system. These sending and receiving control switches move in synchronism so as to control the same groups of subchannels at the opposite ends of the system. An additional stepby-step switch at the sending end is also utilized to control the transmission of a signal pattern and for other purposes.

The switching signals are transmitted on the A and B multiplex channels and during such transmission it is necessary, to interrupt any normal traffic which would otherwise be sent on those channels. The signals sent consist of characters on the B channel which are always blanks and characters on the A channel designated as patterns and confirmations, each pattern being followed by a confirmation. The pattern character by the location of its marking or spacing elements causes the cut-in control relays of the respective subchannels to be operated or released. The confirmation character performs the function of checking the operations performed by the pattern. A blank is also sent on the B channel at the time the switches at the sending end step from their home positions. This blank is used at the receiving end to start the receiving control switch and to check various features of operation. If a subchannel is to be cut in or cut out, a blank is sent on the B channel at the proper time during the rotation of the control switches, followed by pattern and confirmation signals on the A channel and another blank on the B channel. The first blank on the B channel causes the receiving switch and its associated relays to read for the pattern and first pulse of the pattern signal.

confirmation on the A channel. The term pattern is employed with reference to the signal sent to cause the cutting in or out of the subchannel. Of the five pulses in each pattern character, four are employed to operate the cut-in control relays and the fifth pulse is used to stop the circuit under certain conditions of failure. The latter will be considered later. The pattern pulses which are received marking cause the receiving cut-in control relays to be operated and those received spacing cause the corresponding relays to be released so that any single pattern group may cut in or out four subchannels.

The particular subchannel which will be controlled by any pattern pulse will be determined first, by the location of that pulse among the four which make up the pattern and second, by the number of steps the pattern switch has taken from its home position. The sending pattern and control switches are started by the closing of a common test circuit when one of the subchannels is to be changed from the inoperative to the operative condition or vice versa, and as the switches step they test each group of four subchannels to determine whether any subchannel in that group is to be cut in or out. When the switches reach a contact stud corresponding to a group of which at least one subchannel is to be cut in or out, pattern and confirmation signals are sent which of course may cut in or out up to four subchannels upon sending the pattern and confirmation signals of a group only once.

In the initial movement of the step-by-step switches a blank is sent on the B channel which is followed by a guard character on the A channel during the following revolution of the distributor brushes. The guard character consists 'of some combination of marking and spacing pulses which are transmitted each time the sending pattern and control switches rotate and this guard character is tested for accurate reception at the receiving end. The receiving control switch starts to step upon receiving said blank on the B channel and then causes control relays to read for the guard character on the A channel. In a large telegraph system a number of varioplex systems having line terminals at a single ofiice may be employed. In starting up these systems it may be possible to accidentally connect the terminals to the wrong systems which would cause the transmitted signals to be sent to the wrong receiving printers. Therefore different guard characters are selected for the different varioplex systems and the failure to reoeive the proper guard character is arranged to stop transmission. In this manner the system is arranged so that the subchannels of one varioplex system are prevented from working into the subchannels of another system.

The confirmation signal following each pattern signal bears a predetermined relation to the pattern signal and the system is automatically stopped if the proper confirmation signal is not received. The first pulse of each pattern signal is normally sent spacing but is changed to marking when the circuit is to be stopped. The remaining pulses of the pattern control groups control the four subchannels of that group and thus may be either marking or spacing. The first pulse of the confirmation signal is normally sent spacing and is used in conjunction with the The second, third, fourth and fifth pulses of each confirmationsignal are sent with their polarities opposite that of the second, third, fourth and fifth pulses of the pattern signal and are used at the receiving end to confirm the accurate reception of the pattern. Thus if the confirmation signal does not check the previous pattern signal, transmission over the system is stopped.

The confirmation signal is also arranged to check the positions of the chain control relays which should have been operated by the previous pattern signal and thus determine whether the proper subchannels have been cut in or out. If the confirmation signal does not check the positions of the receiving chain control relays set up by the pattern signal, transmission is stopped. The confirmation signal also check the loss of synchronism between the sending and receiving control switches so that the transmission is stopped if the switch at one end of the system gets out of step with the control switch at the other end. The system is further arranged to transmit pattern signals at predetermined time intervals even though there is no change in the pattern of the subchannels. If no pattern si nal is received for a predetermined time greater than the normal interval referred to which might result from failure of the line circuit or other causes, the system is shut down.

The system may also be provided with suitable regulating signals and the like for the use of the attendants at the respective offices. Manual control keys for shutting down the system or'effecting other control functions at will may also be provided as set forth in detail below.

Referring to Figs. 1 to 11 of the drawings, the transmitting ends of four subchannels are shown in Fig. 1 and corresponding printers or receiving devices in Fig. 11. The connector relay chain for connecting the transmitters to the lane of traffic is shown in Figs. 1, 2 and 3. The lane of traffic is shown for purposes of illustration as a three-channel synchronous multiplex system comprising transmitting and receiving distributors shown in Figs. 7 and 8 and associated with line circuit L arranged for full duplex operation in the conventional manner. Signals received at the receiving distributor are connected, through a connector relay chain shown in Fig. 11 and similar to that at the transmitting station, to the printers PI to P4. The auxiliary signalling and control apparatus includes two step-by-step control switches at the transmitting station shown in Fig. 5, one of which is hereinafter referred to as a pattern switch. At the receiving end a similar step-by-step switch shown in Fig. 9 is provided which is operated in synchronism with the control switch at the transmitting end of the system so that corresponding functions may be effected simultaneously at opposite ends of the system. The detailed operation of the system is as follows:

Subchannel circuits The transmitting apparatus of four subchannels is represented at H, I2, :3 and I4 in Fig. 1. The tape transmitter at the transmitting end of each subchannel and intended to represent any suitable source of signals comprises adjustable contacts I5 positioned in accordance with the perforations in the tape and stepping magnet I6 for advancing the tape through the transmitter. The construction of the tape transmitter may be similar to that disclosed in the patent to Benjamin, No. 1,298,440, dated March 25, 1919. An auto-stop relay I1 is associated with the tape transmitter and controlled by the contacts of a tape lever I8 resting, on theloop of tape feeding into the transmitter, the auto-stop relay ll being arranged to lock up the stepping magnet of the tape transmitter in the usual manner when the loop of tape from the tape reperforator shortens.

The contacts I5 of the tape transmitter are connected to the conductors I to 5, inclusive, of a cable 2| and through the contacts of the connector relays 3|, 4| or 5|, to the respective channels A, B and C of the multiplex transmittin distributor as described above. The contacts I5 of each tape transmitter are also connected through series resistors I9 to positive battery. The right hand or spacing bus bar of the tape transmitter is grounded and the left hand or marking bus bar is connected through series resistances 20 to negative battery associated with the control element or grid of a vacuum tube 26. Thus it will be seen that whenever one of the contacts I5 of the tape transmitter engages a marking contact, the potential of the grid of the vacuum tube 26 will be changed from negative to positive potential and the tube rendered conducting for a purpose that will be described below. A shunt condenser 2'! provides a suitable time delay in the fluctuations of the grid potential so that the tube 26 remains conductive during the, stepping of the tape through the tape transmitter although the contacts I5 are momentarily withdrawn from the marking bus bar at each step.

Thus as long as normal code combinations, in which at least one element of the code is marking, are being transmitted through the tape transmitter tube 26 is conductive. However when a blank or all-spacing code combination causes all of the contacts I 5 to engage the right hand or spacing contacts, the tube 26 becomes non-conductive by reason of the negative potential applied to the control grid thereof. When one or more of the conductors I to 5 of the cableZI are grounded through the spacing bus bar of the tape transmitter, one or more circuits are closed through a connector relay of the relay chain for operating one or more of the storage relays BI to 15 respectively associated with the fifteen segments of the segmented sending ring TR. of the multiplex transmitting distributor. As shown, one terminal of the winding of each of said storage relays is connected to positive battery whereby the application of ground potential to the other terminal energizes the relay and at a front contact of said relay connects spacingpotential to the corresponding segment of the sending ring TB of the distributor. However the resistance of the resistors 20 is of such value that when the contacts I5 of the tape transmitter engage the left hand or marking bus bar, the particular ones of the storage relays 6| to I5 connected at that moment to said contacts are not energized.

After the perforation or storage of a message in the tape associated with the transmitter I5 has been completed, it is necessary to step out enough blank tape from the perforator so that the last message character can reach the contacts of the tape transmitter. This is done by automatically perforating blanks in the tape whenever transmission ceases for a predetermined time sufiicient in number to position the last message character beneath the pins of the tape transmitter in the manner shown, for example, in the patent to Hoover et al., No. 1,851,838, dated March 29, .1932. When-another message isto be sentoverthesubchannel, it is desirable to step the blank tape thus formed through the tape transmitter without transmitting said blanks over the line circuit. This is accomplished in the following manner: As soon as the new message is started and the first characters are perforated in the tape, the tape lever l8 drops and closes its contacts Which are in circuit with the left hand winding of the autostop relay It will be understood that during inoperative periods the auto-stop relay is maintained energized by a locking circuit through its armature and right hand winding and the winding of the stepping magnet l6 of the tape transmitter. Thus the last transmitter stepping pulse received by the stepping magnet I8 of the tape transmitter after the contacts associated with the tape lever |8 opened caused the autostop relay I! to be locked up in series with said magnet which prevents further stepping of the tape transmitter. When the tape lever contacts are again reclosed as described, a circuit is closed from positive battery through the interrupter 28, the third armature, and back contact of relay 8|, the outer armature and back contact of relay 82, conductor 8 of the cable 2|, the right hand outer armatures and back contacts of relays 3|, 4| and 5|, conductor 1 of the cable 2|. the armature and back contact of relay 83, the contacts of the tape lever l8, the left hand winding of relay l1 and the stepping magnet i8 of the tape transmitter to ground. Since the relay H is provided with equal differentially-related windings, the closure of said circuit causes the relay to release its armature and open the locking circuit of the stepping magnet l8. Subsequent transmitter stepping impulses flow through the two windings of the relay H in opposition, thus intermittently energizing the stepping magnet |8 of the tape transmitter to step the tape through the transmitter without energizing relay H. In this manner the tape "is stepped through the transmitter as long as blanks are positioned over the pins of the transmitter.

However when a normal character is stepped into the transmitter (having at least one marking element in the code combination), at least one of the contacts I5 of the tape transmitter engages the marking bus bar of the transmitter. The application of positive potential to the grid of the vacuum tube 26 through the resistors l9 and changes the potential of said grid from negative to positive and the tube 26 becomes conductive. When said tube becomes conductive, relay 8| having its operating winding connected in series relation with said tube becomes energized and opens at its third armature and back contact the described stepping circuit of the tape transmitter. The stepping of the tape transmitter ceases until the subchannel is cut in to tape its turn with the other operative subchannels, whereupon the tape is stepped through the transmitter under the control of the multiplex distributor in a manner to be described below. If the contacts associated with the tape lever |8 open because of tight tape before a normal character appears in the transmitter, relay will again be energized bythe current traversing its right hand winding to lock up the stepping magnet of the tape transmitter through the armature and the make-before-break contacts of said relay. When the tape loop between the perforator and the tape transmitter again lengthens, the stepping of blank tape through the transmitter will proceed as before.

Upon the energization of relay 8| as described,

a circuit is closed from ground through the second armature and front contact of relay 8|, the left hand winding of relay 83 and the inner. ar mature and back contact of the relay 82 to battery, whereupon relay 83 becomes energized. The transmitter stepping circuit from the multiplex distributor includes contacts of the chain or connector relays 3|, 4| and 5| since this circuit is only operative after the subchannel has been cut in. If the chain relay 5| is operated to connect the first subchannel to channel C of the multiplex system, a circuit is closed by the multiplex local brushes from battery through the C control segment 87 (see Fig. 7), the conductor 88, the outer righthand armature and front contact of relay 5| (Fig. 3), the seventh contact of the cable 2|, the armature and front contact and the right hand winding of relay 83 and the right hand winding of relay 82 to ground. Thus the first stepping pulse from the multiplex local segment 81 after cut-in has been effected, energizes relay 82 as it is'necessary to divert the first pulse from the stepping magnet of the tape transmitter or the normal character awaiting transmission would be stapped out. Relay 82 is locked up by a circuit extending from battery through its inner armature and front contact, the left hand winding of relay 82 and the middle armature and front contact of relay 90 to ground. Relay 90 is energized when the subchannel is cut in as described below and remains energized as long as the corresponding subchannel is entered on the multiplex system. At the end of the stepping pulse which operated relay 82 in series with a Winding of relay .83, relay 83 becomes deenergized since its original operating circuit is interrupted at the inner armature and back contact of relay 82. The deenergization of relay 83 connects the stepping circuit from the multiplex local segment 81 described above through its armature and back contact to the stepping magnet Iii of the tape transmitter so that subsequent stepping impulses operate to step the tape through the transmitter.

When the connector relay 3| of A channel instead of connector relay 5| of C channel is operated, a similar stepping circuit for the first subchannel may be traced from the A control segment 93 of the local ring of the multiplex distributor through the conductor 94, the second armature and back contact of relay 99, conductor IN, the right hand outer armature and front contact of relay 3|, the right hand outer armature and back contacts of relays 4| and 5|, and conductor 7 of the cable 2| to the armature of relay 83. Similarly when connector relay 4| of B channel is energized, a transmitter stepping circuit for the first subchannel may be traced from the B control segment 95 of the local ring of the distributor, through the conductor 98, the outer armature and back contact of relay I82,

conductor I83, the outer right hand armature and front contact of relay 4|, the outer right hand armature of relay 5| and conductor 1 of the cable 2| to the stepping magnet of the tape transmitter.

The foregoing description explains how the blanks perforated in the tape are withheld from transmission over the line if they precede the actual connection of the subchannel to the multiplex system. As soon as a normal character is positioned over the pins of the tape trans mitter, the automatic stepping of the transmitter stops until the subchannel is cut in whereupon the stepping of the tape transmitteris controlled in timed relation to the operation of the multiplex distributor by control segments 81, 93 and 95 of local ring of said distributor. If further blanks occur in the tape after the subchannel has been cut in, these blanks will be transmitted over the line circuit until the subchannel has been cut out after which further blanks in the tape Will be deleted as described above. 7

At the receiving end of the system the four subchannels are represented by four receiving devices or printergPI, P2, P3 and P4, Fig. ll. These printers may be start-stop telegraph printers connected through individual conductors extending from branch or patrons offices to the local main office of the system. In order to operate said printers in accordance with the characters received over the multiplex system and stored on the storage relays 2II-285 of the receiving bank, stored signals in the form of fiveunit code combinations are converted into sevenunit or start-stop signals. The storage relays 2' to 285, inclusive, are arranged to control the transmitting relays 235, 236 and 23'! associated with the respective channels of the multiplex system. The line circuit from each printer as shown is connected through the normally closed contacts of the make-before-brak contact set of the outer armature of each receiving connector relay, such as the relays 23I, 24I and 25! of thefirst subchannel, The contacts of relay 25I are connected to negative battery to maintain a rest potential upon the operating magnet of the printer PI when the first subchannel is inoperative and the relays 23I, 2M and 25I are deenergized. The receiving connector relays of the other subchannels are similarly arranged. When one of the connector relays 23I, 24I r 25I is operated, the circuit of the printer PI is extended through the outer. armature of the operated relay, for example relay 23I and the armature of relay 235 to negative battery in order to permit the latter relay to impress the start and selecting pulses on the printer magnet. In a similar manner the relays 2M and 25I when energized connect the printer magnet to the contacts of relays 236 and 231 of the B and 0 channels of the multiplex system respectively. Similarly the connector relays of the other subchannels are arranged to transfer the circuit of. the respective printer magnets to the particular control relay 235, 236 or 231 corresponding to the channel of the multiplex which is to be connected at that moment to a particular printer. The printers PI to P4 may also be provided with conventional signal and motor control features which are omitted for the sake of simplicity.

Connector relay chain or mixer The connector relay chain or mixer for four subchannels at the transmitting station comprises the connector relays 3| to 34, 4| to 44 and connector relays for each multiplex channel are arranged in series relation and it will be obvious that as many more subchannels may be similarly connected as desired. Likewise in a multiplex system employing more or less than three chan- The specific relay chain illustrated is nels, other vertical sets of connector relays may be added in a manner that will be obvious from the following description to provide for connecting a series of operative subchannels to any desired number of multiplex channels in order. If the number of operative subchannels is not greater than the number of multiplex channels available, three in this instance, the relay chain does not step during the cyclic. operation of the multiplex distributor. -In the following descrip tion of the relay chain this special case will be considered first.

The operation of cutting in the first subchannel results in the energization of relay in a manner to be described below. Upon theenergization of relay 90, a circuit is closed from ground through the outer right hand armature and front contact of relay 00, the winding of relay I05, conductor I04 and the third right hand armature and back contact of relay I06 to battery, whereupon relay I05 becomes energized. Each of the other subchannels is similarly provided with a chain control relay I01, I08 and I03, corresponding to the relay 90, and said relaysare likewise operated when the corresponding subchannel is cut in and released when the subchannel is cut out. The energization of any of the relays I01, I08 and I09also effects theenergization of relay I05, which thus remains energized as long as any subchannel is cutin.

Assuming that the third subchannel has been cut in, upon the energization of relays I08 and I05, when the brushes B3 of the multiplex transmitting distributor connect battery to thelocal segments I I I or I I2 of the right hand local rings, a circuit is closed from said battery through the conductor H3, the armature and front contact of relay I05, conductor H4, the inner left hand armature and back contact of guard relay I22,

conductor II5, the inner right hand armature and back contact of relay I09, the inner right hand armature and front contact of relay I08, conductor -I I6, the right hand operating winding of relay'53, the winding of guard relay I23 and resistor II9 to negative battery, whereupon relays 53 and I23 become deenergized. Relay 53 looks up through a circuit extending from negative battery through the winding of relay I23 and the locking Winding of relay 53, innerleft hand armature and frontcontact of relay 53 and the rectifier I33 to ground thus maintaining the relays 53 and I23 energized after the end of the operating pulse from the multiplex distributor.

Each time the brushes of the multiplex transmitting distributor make another revolution, the described circuit of relays 53 and I23 is reclosed and the third subchannel remains connected to C channel of the multiplex system. If either of the other subchannels had become operative instead of the third subchannel, this subchannel would likewise have been connected through connector relays 5|, 52 or 54 to 0 channel of the multiplex system. The operating circuit of the fourth connector relay 54 for example, may be traced as follows: from the local segments III and II2.,of the right hand local ring of the distributor throughthe conductor I I3, the armature and front contact of relay I05, conductor I I4, the inner left hand armature and back contact of relay I22, conductor II5, the inner right hand armature and front contactof relay I09,

conductor I H, the right hand operating winding of relay and the winding of relay I23 to negative battery. In a similar manner the operating chain pulse from the C channel local segments t'acts of the operated chain control relay 90 or I ill to the'connector relays or 52 when the first or second subchannel is operative. It will be noted; that when a subchannel is first connected to the multiplex system it will be connected through one of the connector relays 5I to 54 of thefC channel group since the connection dia gram shown is arranged to send the first characterir'om an operativesubchannel over the C channel of the multiplex system. This and various other detailed features of the wiring shown are merely a matter of choice and are not essential.

Whe'n a connected subchannel for instance the third subchannel is to be cut out, the corresponding chain control relay such as relay I08 becomes deenergized and causes relay I05 to become deenergized. The next succeeding chain impulse from the local segments III and H2 of the distributor is connected through the conductor II3, the armature and back contact of relay I05 and the conductor I I8 to the upper end of the resistor H9 in the locking circuit of relays 53 and I23. Thereupon the current in the winding of relay I23 and the locking winding of relay I53 drops to zero and said relays are deenergized, the rectifier I33 preventing reversed flow of current from the locking ground to positive battery at the local ring of the multiplex distributor. The other connector relays in case one of the other subchannels is to be cut out are unlocked in a similar manner upon the deenergization of the chain control relay 90, I61 or I09 and relay I05.

If three subchannels are cut in simultaneously, these subchannels will be connected to separate channels of the multiplex system. Thus if the multiplex distributor rotate, this relationship of the first three subchannels to the multiplex system is not disturbed and the three subchannels remain connected to channels B, A and C, respectively of said system. It will be noted that each of the three chain relays of a particular subchannel is provided with contacts which shortcircuit the'operating windings of the other two relays of said group. By reason of this arrangement and the other connections shown it is insured that during the operation of the mixer or relay chain shown there will never be more'than one relay operated inany vertical row or in any horizontal row. Thus there can never be more than one subchannel connected to a channel of the multiplex system or a subchannel connected to more than one channel of said system.

When any multiplex channel is idle, the letter X (#2 spacing-code combination) is sent continually over said channel. The sending relays Iil to 15, inclusive, are disconnected from all transmitters when the multiplex channels are idle. However when channel A for example, is not connected to any subchannel transmitter, connector relays 3I to 34 and the guard relay I2I are deenergized. A circuit is closed, therefore, from ground through the right hand armature and back contact of relay I2I, the conductor I4I, the second conductor of the cable 60, the fourth right hand armature and back contact of relay I42, Fig. 6, conductor I43 and the winding of sending relay 62, whereupon the latter becomes energized to apply spacing potential to the second segmentfof the transmitting ring of the multiplex distributor so that the letter X is transmitted on A channel as long as the channel remains idle. Similarly if no subchanrespective connector relays are in shunt relation to the operating circuits of the other relays in each vertical group. Therefore, since the respective connector relays are locked up to ground potential at the rectifiers I3I, I32, I33 and I34, the application of a positive operating pulse from the chain control segments III, II2, I25 or I35 of the multiplex local ring at the right hand or negative potential end of the locking winding of any particular connector relay reduces the current to zero in the locking winding of said relay. Thus any connector relay which is locked up to connect one subchannel to the multiplex system is released whenever another connector relay of the same vertical group is operated to connect another subchannel to the same multiplex channel.

If we assume that the first subchannel is connected to channel B of the multiplex through connector relay 4!, the second subchannel is connected to channel A of the multiplex through connector relay 32 and the third subchannel is connected to channel C of the multiplex through connector relay 53 in the manner described above, and the fourth subchannel is out in by the energization of relay H39, this subchannel will take its turn with the other three subchannels in transmitting over the multiplex system. When the C chain pulse is applied to the conductor H3 from the local ring of the distributor under the assumed conditions current will flow from positive battery through said conductor, the armature and front contact of relay I05, conductor H4, outer left hand armature and front contact of relay 4|, conductor I46, conductor M7, the outer left hand armature and front contact of relay I23, conductor II5, the inner right hand armature and front contact of relay I59, conductor I I1, the right hand operating winding of relay 5% and the Winding of relay !23 to negative battery, whereupon relay 54 becomes energized and locks up through the above described locking circuit including the rectifier I34 and relay I23 is maintained energized. As stated above, however, the positive operating pulse for the chain relay 54 causes the chain relay 53 which had been previously locked up to be released since the locking circuit through the lefthand winding of relay 53, the left hand inner armature and front contact of said relay and the rectifier I33 is in shunt relation to the operating circuit of relay 54 and the rectifier I33 prevents the current in the locking winding of relay 53 from reversing. It should be noted that if the rectifier I33 were not provided, at the instant when relay 54 operated and before relay 53 has had time to release, the locking winding of relay 54 would form a path for an inductive surge of current resulting from the decreasing current in the locking coil of relay 53. This inductive surge would tend to reduce the rate of fall of magnetism in magnetic circuit of relay 53 and said relay might not release in the interval of time during which the local brush B3 is on the segment III or H2. However the rectifier I33 suppresses this surge of current and the relay releases its armatures practically instantaneously. It will be apparent that the operating and locking circuits of the respective connector relays in each vertical row are similarly arranged so that the operation of any chain relay unlocks any previously operated chain relay in the same vertical row.

The operation of relay 54 and release of relay 53 disconnects subchannel 3 from channel C of the multiplex andconnects the fourth subchannel to said multiplex channel. When the brushes B3 of the distributor engage the A chain segment 825, the chain pulse through conductor I26 operates chain relay 33 and releases the locked up chain relay 32, whereby the third subchannel is connected to channel A of the multiplex in place of the second subchannel. Similarly the B chain pulse from the distributor operates chain relay 32 and releases chain relay 4! to connect the second subchannel to channel B of the multiplex in place of the first subchannel and so on, whereby each subchannel will be connected in order to the multiplex channels in a manner ependent upon the number of operating subchannels.

The connector relays at the receiving station and the control circuits therefor from the local ring of the multiplex receiving distributor are arranged in identically the same manner and under the control of a series of chain control relays corresponding to relays 90, I01, etc., of Fig. 1. These control relays are indicated diagrammatically in Fig. 11. The connector relays of the receiving relay chain are thus operated in the same order as the chain relays at the transmitting station to connect the printers PI to P4 to the respective multiplex channels to record on each individual printer the intelligence signals which are sent by the corresponding transmitter at the transmitting station.

subchannel cut-in control The cut-in or cut-out of a subchannel is effected automatically under the control of the autostop contacts controlled by the tape lever I8 of each subchannel whenever transmission is to be started or has been completed, respectively. As pointed out above, closure of said contacts upon the lengthening of the tape loop to the tape transmitter and the positioning of a normal character over the pins of the transmitter cause relay SI to be energized. Relay 8I becomes deenergized again when the characters perforated in the tape have been transmitted and the tape lever l S is raised to open the associated contacts. The energization of relay BI when the chain control relay 9!] is deenergized closes a common test circuit which starts the control switches at the sending and receiving ends hunting for the group of subchannels in which the change in the subchannel pattern is to be made. The common test circuit is likewise closed at the end of transmission to effect a similar result when relay 8| becomes deenergized and relay is energized. The pattern switch at the transmitting station comprises a rotary step-by-step switch having a stepping magnet I50 and six wipers I6! to I 66 each adapted to engage a series of bank contacts. The control switch at the receiving station which is stepped in synchronism with the attern switch comprises a stepping magnet 260 and movable wipers 26I to 265 operated thereby. In addition a step-by-step control switch is provided at the transmitting station comprising an operating magnet I10 and wipers IN to I16 controlled thereby.

Assuming that the first subchannel has been idle and relay 8| becomes energized, as described above, in response to the lengthening of the tape loop at the transmitter of said subchannel, the test circuit which initiates the operation of the pattern and control switches may be traced from ground through the outer left hand armature and back contact of relay 90, the outer left hand armature and front contact of relay BI, conductor I50, resistor II, the left hand armature and back contact of relay I06, conductor I52, wiper I15 of the control switch in its home position to the grid of the vacuum tube I54 which is in series relation with a relay I55. When ground potential is applied to the grid of said tube the tube conducts current and causes relay I55 to become energized. The gridof the vacuum tube I54 is connected to negative battery through the series resistors I56 and I51, and is controlled by the negative charge on the condenser I58 whereby the tube is normally non-conducting. The charge on the condenser I58 m-ay leak off through the shunt resistor I56 after a predetermined period of time to permit the tube to become conducting but under ordinary conditions the tube is rendered conducting by the closure of the common test circuit. However even if no subchannel seeks to cut in or out for a long period, the relay I55 is operated periodically, for a purpose that will be explained, by the timed operation of'the tube I54.

Upon the energization of relay I55, the associated signal lamp I59 is lighted to indicate that the pattern signal has been initiated and a circuit is closed from ground through the armature and front contact of said relay, the wiper I16 of the control switch, conductor I11, left hand outer armature and back contact of relay I18, the right hand outer armature and back contact of relay I19, conductor I80, resistor I8I, left hand or operating coil of relay I02, the third armature and back contact of relay 99, conductor I62, wiper I1I of the control switch and conductor I83 to the local segment I84 of the left hand local ring of the transmitting distributor. As soon as the multiplex brushes B2 engage the local segment I84 the above described circuit is connected to positive battery at the local ring'of the distributor, and relay I 02 becomes energized and locks up through its right hand locking winding and its inner armature and front contact. It will be noted that by reason of the position of the local segment I84 on the distributor, relay I 02 becomes energized shortly after transmission of a character on B channel of the multiplex system.

When the brushes B2 of the distributor engage local segment 95, a circuit is closed from positive battery through said segment, the conductor 96, the outer armature and front contact of relay I02 and the left hand operating winding of relay I65 to ground whereupon relay I85 becomes energized and locks up through its locking winding and its inner armature and front contact. The operation of relay I85 sets up a blank on B channel of the multiplex since the outer back contacts of storage relays 66 to Which normally impress marking potential on segments 6 to I0 of the transmitting ring are connected through the conductor I81 and the middle armature and front contact of relay I85 to spacing battery so that even if one or more of said relays is in the marking or deenergized position, spacing battery is connected to the segments of the transmitting ring. Therefore upon the next revolution of the brushes of the transmitting distributor, a blank or all-spacing code combination is sent to initiate the operation of the pattern switch at the receiving ofiice. Spacing battery potential is normally connected to the front contacts of the outer armatures of relays 66 to 10 of B channel through the conductor I 88. When relay I85 is deenergized, marking battery is connected through the middle armature and back contact of said relay and the conductor I81 to the back or marking contacts of said storage relays of the B channel.

It will be noted that the operation of relay I02 as described, diverted the B channel transmitter stepping pulse from segment 95 of the local ring to the winding of relay I85 and thus prevented the stepping of the transmitter which would normally have operated over the B channel. This withholds the transmission of the character set up on this subchannel so that the blank can be sent on B channel by the operation of relay I85 as described Without losing the character which would normally be sent from a subchannel over said multiplex channel since this character will be Withheld for transmission at the next opportunity presented to the' subchannel.

During the next revolution of the brushes of the multiplex distributor, a circuit is closed through the local segment I89, conductor I90, the first conductor of the cable I9I, wiper I6I of the sending pattern switch in its home position, conductor I92 and the second left hand armature and back contact of relay I42 to the negative terminal of the locking winding of relay I02 whereupon relay I02 becomes deenergized. A circuit is then closed through local segment I95 of the transmitting distributor, the conductor I96, the wiper I12 of the sending control switch in its home position, conductor I91, the armature and front contact of relay I85 and the right hand operating winding of relay 99 to negative battery'whereupon relay 99 becomes energized. At the end of the described operating pulse for relay 99, said relay becomes locked up through its inner armature and front contact, its left hand locking winding and the Winding of relay I42 whereupon relay I42 also becomes energized.

The operation of relay I42 connects the circuits of the sending relays 62, 63, 64 and 65 of the A multiplex channel through the first four right hand armatures of said relay and the cable I9I to the wipers I63, I64, I65 and I66 of the sending pattern switch. When the switch is at its home position as shown, a guard character is set up on the A channel upon the operation of relay I42 and this guard character is transmitted in the next revolution of the distributor brushes following the first blank on B channel.

It will be noted that the operation of relay 99 opens at its second armature and back contact the transmitter stepping circuit for the subchannel transmitter that is connected to the A multiplex channel, when the guard signal is to be sent over this channel, so that the character which would normally be sent over the A channel will be deferred until the subchannel transmitter is again connected to the multiplex system. This operating circuit for the transmitter includes conductor 94 and local segment 93 of the distributor. It will be apparent that each time a control signal is transmitted over A multiplex channel, the subchannel transmitter stepping circuit is opened in a similar manner to defer subchannel transmission during the transmission of the control signal.

As indicated the guard character in this particular instance consists of the code combination having the third and fifth elements spacing, since the storage relays 63 and 65 will be energized by the ground potential on the first contacts associated With the wipers I64'and I66 of the pattern switch. In accordance with one feature of the 

